The present invention relates to a method for separating barium from water-soluble strontium compounds.
The most important mineral used as a raw material for the production of strontium compounds is celestine. It consists predominantly of SrSO.sub.4 and is usually contaminated with barium compounds. In order to use strontium compounds in certain sectors of industry, e.g., in coating television picture tubes and also in medicine, substantially barium-free strontium salts are often required. It is therefore necessary to separate or remove the naturally occurring barium content from strontium salts.
Methods for reducing the barium content in strontium compounds are already known. According to H. Caron and D. Raquet, Bull. Soc. chim. (4), 3, pages 493 to 495 (1908), the barium content of an SrCl.sub.2 solution contaminated with 25% BaCl.sub.2 can be reduced to 1% by adding SrSO.sub.4, allowing the solution to stand for 48 hours and subsequently filtering. Further removal is effected by precipitation with K.sub.2 CrO.sub.4 /K.sub.2 Cr.sub.2 O.sub.7. With this method, contamination of the low-barium product with the toxic chromate may occur.
L. Barthe and E. Falieres, Bull. Soc. chim, (3), 7, pages 104 to 108 (1892) report on several compounds, which have lead to unsatisfactory results. These include reaction with hexafluorosilicic acid, carbonates, sulfates (inter alia, SrSO.sub.4) and with sulfuric acid of varying concentration. These authors recommend a method of separating barium by adding SrSO.sub.4 to a strongly hydrochloric acid solution of SrCl.sub.2 containing BaCl.sub.2. This method, however, requires a subsequent reaction phase of several days.